Field of the Invention
The present invention relates to an image heating device such as a fixing device mounted on an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer.
Description of the Related Art
On an image forming apparatus such as a copying machine or a printer using an electrophotographic method, a heating fixing device is mounted, which heats a recording medium (hereinafter referred to as a “recording sheet”) on the surface of which an unfixed toner image has been formed, thereby fixing the unfixed toner image onto the recording sheet.
In the image forming apparatus, when recording sheets (small-size sheets) have widths smaller than that of a recording sheet having the maximum width size that can be used in the image forming apparatus, and if the small-size sheets are continuously passed through the image forming apparatus, and printed, a so-called temperature rise in a sheet non-passing portion occurs in which the temperature rises excessively in the area of the fixing device through which the small-size sheets do not pass.
As one of the techniques for addressing this problem, Japanese Patent Application Laid-Open No. 2003-317898 discusses a method for sandwiching a highly thermal conductive member between a heater and a supporting member of the heater.
If, however, the heater is attached to the supporting member when an apparatus is manufactured, the highly thermal conductive member is hidden behind the heater. Thus, even if the attachment of the highly thermal conductive member has been neglected, the neglect of the attachment may not be noticed.
Further, to sufficiently bring out the effect of the highly thermal conductive member, it is necessary to properly attach the highly thermal conductive member between the heater and the supporting member. However, particularly if a thin highly thermal conductive member such as a graphite sheet (the thickness of a graphite sheet is about 20 to 400 μm) is used, the sheet may be folded due to the thinness and the highly thermal conductive member may not be able to be properly attached when an apparatus is manufactured.